Wave length modulation



ZAT/95,859

Aug. 23, w49., L. E. NORTON WAVE LENGTH MODULATION Filed Aug. v 25, 1945bhbbbbh 1111111 NVENTOR man? /bffafz ATTORNEY Aug. 23, 1949.

Filed Aug. 25, 1945 L. E. NORTON WAVE LENGTH MODULATION OJC.

2 Sheets-Sheet 2 Ann vu" ff Loa/@ll E. Vario/1 BY gw ATTORNEY INVENTORatentec ug. 23, 194g WAVE LENGTH MODULATION poration of Delaware ofAmerica, a oor-V out the need of filters in all cases except where avery wide frequency deviation is to be accomplished. In such cases as,for example, in case the deviation frequency approaches the Acarrierfrequency, an extremely large number of components appear in themodulation output close to the :useful fundamental. To overcome thisdefect I provide an embodiment wherein the modulators are differentialinstead of single ended. In the differential modulator outputs then, asstated above, the components appear in pairs to cancel to zero, leavingonly the fundamental carriers which are combined in parallel andsupplied to the load.

The above advantages and others, and the manner in which they areattained will be apparent from the description which follows.

In this description reference is made to the attached drawings whereinFig. 1 illustrates mainly by rectangles the essential elements or unitsof a phase or frequency modulation system arranged in accordance with myinvention.

Fig. 2 illustrates details of one embodiment of mymodulation system,while Fig. 3 illustrates a modification of the arrangement of Fig. 2 vtobe used where the deviation frequency is very high.

vIn the drawings, Fig. 1, lil is a source of oscillations of constantwave carrier wave frequency having a frequency of say F=W/21r. Thesource l may be conventional and may comprise if desired a stabilizedoscillator such as a crystal oscillator and/ or frequency multipliers.The output of the oscillator I0 is supplied to two coupling andisolating and/ orA amplifying stages T1 and T2. One of the stages issupplied substantially directly from I0 while the other stage issupplied by way of a transmission line L having a time delay anglerepresented for convenience by the Greek letter 3b. The stages T1 and T2prevent coupling of the two channels by way of the source l or circuitstherein. These stages also permit adjustment of the gain through thechannels so that the gain through T1, for example, is about equal orsubstantially equal to the gain through T2 and its delay line. The delayline L may comprise antarticialline or network, a transmission line, ora wave guide. l

The. stages T1 and T2 may comprise amplifier tubes of substantiallyconventional design having their input electrodes excited by phasedisplaced oscillatory energy from l0. The potential applied to the inputcircuit of T1 is e=E (l-l-m sin wt) (1) and that applied to the inputcircuit of T2 is e1=E[1-|1n1 sin (wt-H0] (2) where 5b is the delay angledue to the line L, E is the peak or maximum alternating current voltagefor m=1 and m is the modulation factor. In these equations and thosewhich follow E repreE sents peak or maximum alternating voltage from theoscillator Il) for m=1 at frequency f=w/21r. The factor m represents allVariations from this peak initial Vvoltage including in later equationsVariations caused by modulation. subscripts are used with 1n. to denotedifferent modulation factors when the same may be used, like subscriptsbeing used to denote the same modulation factors where such must beused. For example, in the Equations 1 and 2 different modulation factorsmay be used. For convenience and toV simplify the description andfacilitate understanding of the invention E has been so chosen that thevariations m are always positive, that is, in the anodecathode circuits,take place about a base line sufficiently above zero potential as to bepositive at all times. This will be referred to again later. It is alsoconvenient to make the modulation factor m1 equal the modulation factorm. In practice it would be substantially equal since both currents comefrom the same source l0, and the tubes are alike.

. The output potential from tube T1 is then e1=1cE (1+m sin wt) 3) andthe output potential from T2 is ca 461 Ell-l-m sin (wt-{10)} (4) Inthese equations lc represents the gain of stage tube T1 and k1represents the gain of tube stage T2.

It is convenient to make k=1c1 which is done by adjusting the gains ofthe stages and then e3 becomes The output of stages T1 and T2 issupplied Yto the first and third grids of tubes in the next stages ofthe two channels as will be seen by reference to Fig. 2. A modulating ormixing or converting action takes place in these stages and they havebeen referred to as modulators since modulation product terms appear inthe output.

The potential e2=kE(l-{m sin wt) is applied tosay the third grid I4 ofM1 through a coupling condenser I6. A voltage ez' of opposite phaseequal to lcE(1-m sin wt) is applied to the first grid I8 by way of acoupling condenser 2B. The last voltage may be provided in any one ofvarious known ways. For example, the stage T1 tube may supply phasedisplaced output by coupling to an anode impedance and to a cathodeimpedance, or the tube anode may feed the primary winding of atransformer having a differential secondary winding. In consideringthese voltages it is to be kept in mind that the average Voltage say Eis above zero an amount such that it does not swing negative. y

In like manner a voltage is 'applied to the third grid 24 of the tube instage M2 by a coupling condenser 26 while a phase reversed voltagee3'=lcE[1-m sin (wt-Hw] is applied by the coupling condenser 28 to thefirst grid l30 of this tube.

The modulators M1 and M2 must be operated on the linear portions oftheir characteristics and this is assured by the use of proper gridbiasing resistors 34 and 35,V proper plate source 38, appropriate plateresistors 49 and 42, proper screen grid sources 44 and 46, and cathodereturn resistors 50 and 52 shunted by R. F. bypass condensers. A commonsource of direct current potential may replace the several sources whichare shown separate for convenience and to simplify the connections. Infurtherance of the need of linear amplification it is preferable to usetubes of the type SSAT or 6L'7, if the amplification is done at very lowlevel (with possibility of nal large linear amplification). At higherlevel amplification one may use tubes known in the art as types 802,803, 804 and 807, all operated with input potentials applied to controlgrid and screen grid. For this operation the modulation .factor can notbe made too large (probably always less than 0.5) or the interactionbetween grids will be serious.

The requirement is the same in all cases; i. e.

arm-seca s? tuls lin" whicl'i the grid-to *grid transciiductane issmall. This is metiriltle6SA7\and"6L7 by' extra shielding or screening`grids. The types 802, 837, 804, cosechar; have-fthelextrascreeningvgrildsso they must be operated at smallermcs-duiation'fautore'3 l It would 'be possible to omit modulators(mixers) M1 and M2 and apply the outputsor T1 and T2 to the modulatortubes T3 and T4 directly. HoweventheA useiulphasel'ishift will only be1b.' It is possible to make 1b become 21p by one frequency'riultiplication.^ On' irie'ncy' nnflulti plication is used in thedescription W ich"fo1 lows although obviously more multiplication may beused. A A A As stated above, the potentials 'applied 4to the grids 'I 4and l 8 'of tube M1 areI respectively ezzkmviatmlsiratf- '(6)5@lisci-(3)11 and @Erstimarsan 7) Thepotentials applied tothe gridsw24and 30 and theV output of is e5=^k5Ef1 m2 S1112 (af-1mm:

grandma] 11) To, make ks equal the gains of stages M1j and M2 areproperly adjusted by relative adjustment of the value of the gridbiasresistances 34 and4 3("or A of the potential sourcesfetc'., as iswell known in the'radio art. A Y l The outputs e4 (Equation `10) and'ee(Equation 12) appear at leads 56= and S10 respectively Figs. 1 and 2,'and' are `fed tothe stagesTa and T4 wherein variation of---the R. F.voltages lbythe-- signals is accomplished y d Ifgdesired more A`stagesof frequency-'multiplif cationY may be added to -make l21a become 11p-orlarger.l 1 A. y 1 Y The stages wherein `"the -signal--fmodulationi isapplied to the carrier-to^relatively A'or' difieren` tially modulate`the amplitudes 'ofthe 'phase dis-4 placed voltages =e4- (Equation 110)`and 'es' (E'quafA i tion '11) are shown at T3 and T4 in Figsl "1 andAs? 4'shownl 'in l Fig;-V 2 thesestags each -f"comprise ya multigrid''tuben '(preeialdlyone of'theftyp'e'lis'ted' above). The tube'ofstzag'eTa hasl a :cathode bias resistance '62, a Vgridfbia's v'resistance-`64,a plate source 66, a plate impedance," a'sc'ireer'iV grid sourcel0, and resistance 12. The stage T4 comprises a similar tube withsimilar connections and sourcesto which reference numerals corresponde"ing to those used in stageV T31-|10 have been appiied. These Vtimestages like me tribes M11 arid M2 are operated on the linear portions oftheir characteristic curves'fby the use"`of potentials and resistancesof proper value. The gains o f the tubes are als'o' set vto provideoutputs 'which are '1 substantially of equal magnitude.`

ferentially vbymo'dula'tion currents Yor potentials from the"modulationsource 81 by way of modulationcouplingfcondcnsers and '92.

If now modulating or biasing potential, from sourcel'l, y

` e6=VEs1`1 +`msf(t)] (13) where f(t) is the modulation frequency termwhich is time'. dependent'and where f(t) 1 since,

1 Qin +1111# (1)] Lil +1111. f 1) COS and 15) :If the period of f(t) islong'as compared to :a frequency selective @circuitmay be placed inV theoutput circuit of Ta to reject the potential The filtering `required isvalmost inherentv in the circuit unless special pains are taken toprevent it The period of thev modulation f(t) is likely to be at audiorate, or, atleast very low Vas compared tojtliat" of the high -frequencyoutput. i Therefore, if-inpedances 68 and 18 inthe anode-cathodecircuits of tubes T3 and T4 respectively, have proper impedances overthe range of high frequencies used, the same vimpedances are likely tohave (or can be made to have) approximately zero impedance at the lowmodulation frequencies and only useful output will result.

If the modulation frequency is low as compared to the carrier frequency,impedances 68, 'I8 may easily be made to have a high impedance atcarrier frequency and approximately zero impedance at'thelow'mo'dulationfrequency. This condition is the normalcondition.v v

If the period of f(t) is not long as compared to original vpotentialIch?? cos 2er,

To change to the balanced' modulator arrangement of *Fig-' i 3 the*Output `oflV11 is arranged to supply differential or pushpull R. F'.excitation to the stage T3. The arrangement of Fig. 3 tlrIrm'a'yY-beasillustrated irl'Figs. 1 and 2 as far as the source I@ and stages T1 andT2 and the inputs to stages M1 and M2 Iare concerned. The output iofthe' tubes 'o stages vM1 and M2 may each include the primary winding ofa transformer having a differential secondary 'Winding feeding thefollowing stages T3 and T4' respectively. .Other means such 'as phaseinversion as described hereinbefore in connection with stages add'tothe'v output of T3 the T1 and T2 for converting from Vsingle ended todouble ended translation may -be used. In the balanced modulators T3 andT4' reference numerals corresponding to those used in describ-A Theoutput potential of the balanced modulator T3 is obviously Y Forconvenience makeV ks=k1 by relatively adjusting the gains of T3 and T4.'If the original potential Y MEL; s 2wt is added to the output potentialea the result is the same as that for ev in Eq. 15 but with thetroublesome, unwanted term removed, all without any restriction on therelation between f(t) and 2wt, and without use of a frequency f(t)`Correspondingly, if f(t) wt then modulator T4 is also as shown in Fig.2. The input potentials supplied to grids 8l and 89 of T4 arerespectively es'=Ee[1-msf(t) l (17) and It is convenient to make lc9=ksagain by adjustment of the gain of the tubes.

Here, as in the output of T3 (Fig. 2) a frequency selective circuit inthe output of tube T4 rejects potential 2 2 e,e'=k.E 1 1% cos www] Theoutput of T4 is `grids B9 Forconvenience makeJcm--lca If, as before, anoutput (original) Y potential 2 kmEm ccs (2m-tap) added to em the:result is the same as the rpotential e9 in Eq. 18 but with the lowfrequency vterm Y eliminated Without use of a low frequency rejectioncircuit.

l The original potentials may be addedto the outputs of Ta and T4.'respectively as illustrated in Figure 1. Output including the componentis taken from`stage Tiand applied through decoupling resistance R4 totheoutput combining resistance Re. Output including the component 2 kmE%cos (zowat) is taken from stage T2 and fed over resistance R5 to thecombining `resistance Ra. It is not actually necessary to add thesepotentials. The circuit will operate without them. By so doing I maythen use the same algebra in Equations 20, 21, and 22 for the two casesof tubes T3, T4,

y fand T3. T4. If the two extra potentials are not added, a very similarresult to Equations 20, 21, and 22 appears, but with an unimportantdifference due to the diiierent resultant modulation factor. Theconnections including R4 and R5 1 used to supply.- the said originalpotentials are used only when balanced modulator stages T3 and T4 areused as in Fig.V 3. In the other embodiments these circuits are removed.

In Fig. 2 the outputs of tubes Ta and T4 are -coupled by couplingcondensers |00 and llll and resistances'Rr and Rz'to the common loadresistance Ra, while in Figg the anodes of the differentially excitedtubes in` each stage Ta' and T4 are tied in parallel and then coupled inparallel toA load resistance Rs by coupling condensers |00 and H0 andresistances R1 and R2. The outputs of T3- and T4 of Figure 1 arecombined in parallel (subtracted), in such a manner that the fundamentalcarrier and its modulations only are left. The outputs of T3 and T4' areeach combined in parallel or added algebraically so that all componentsexcept the fundamental carrier and its modulation components add to zeroand disappear from the output without the use of lters. The usefulcomponents appear in the load Ra. The values of R1 and R2 are made equaland much greater than the value of Ra to prevent reactive coupling ofthe output of T4 or T4 to T3 or Ta and vice versa.

The outputs of T3 and T4, as of T3 and T4', are combined in the circuitcomposed of to prevent interaction. The combined output is v ,m2 m211=k11E{2( 1 maf (0] COS 203i 'l' .aszese As usualThe.;onlyidifferenceis that the magnitude of the .yrablephase angle isdiierent.

t "Itis, noted that`in! Fig. 2 the modulation from -ndihe nurrlerlalvelue. fit) 1S also seurtea1isapp1-ieu to third'grids 1s and sa of v to-,the.rstgrids 1l and 8l whereas in Fig. 3 the 13nd. -Yalble Wlih .tlme-...Rewriting Equatlon 20 [,mcdmatibi .isappiiedito Athenrst .grids andthe m2 l radis vitageis applied to the. third grids' of 61,1.=k1V1E[21-7` .tubes-Tsiandi-T42" Bothmethods of operation lmo.; 1 constant m2 10,arel correct andk .the` results are identical. -2-1/44-2m6f (t) v12 (-1.1005 2t). ein ,-iWhet I claim` is:

2 1. The methodof producing alternating cur- I{2wt.tan-1([1 msin 2i-tan(21) .rentmodulated as to timngin accordance with .1' l isi'gna1s...which includes. these steps, generating or its equivalent 15g alternatingcurent... of carrier. 4wave frequency In either case theincremental instantaneous .which is of .substantially `fixed frequency,sepaffrreflllenCy iS equal t0 the time rate of change. 0f rating 'thealternating current into two portions phase angle; Designating-theinstantaneous inof about like hintensity, phase displacing the a1-cremntal frequency by F1 .tenating current ofv one portion elativeto the"[1 menwsin w 25 alternating'curxent of the other portion, derivingFFH-tanjllmm cos 21.4 (23) ffrom said one and said other currentportions f l phase opposed currents multiplied in frequencyfrom,Equation 23 by llike' amounts, mixingthe phase opposed cur- A.or 35y rents ieriyed` .from the ,one and Vother. .current dnV`i1gcmtions,'selectingr the sum ,ordouble frequency msinztifcl (24)lzur'reiits resulting. -.fr om each migraine ste?differentrallmamplitude inodulat ing` e selec ed cur-1+[m"f(t)]2+{1-[T'f (wm COS 2'# fnepnvts, andfso .addinglthe resultantalternating V.From EquatiQnZl it is evidnthat ,the nstn-.4ogcug`rrents-tuatl eil'feompqneiitsjexeept the funda-;teneeusgincremenial lfrecluency varies directly menta!carrieranqitsphaseetfrequency medu- Qiiiththe time. rate. .OflC-llalg '1ioncoinppnentscancel.

` d ."lfheinjftliodofh`fpr0dl1malternating curif (5)] rrent modulated:a'stoftirning in accordance with l5451 ignals which includes 'thesesteps,separating Alem 1f cosJ2\// 1s chosen so as not to depart too'altelnatg Climent :of` Substantially fixed frefFlsreetlr @muniti thensuene-firewire.persons or aber@ ike intensity, m6 .d 2 ase displacingthealternating current of one Fi f2-,im Zf 0] 5) portion' relative tothe alternating entrent of the 550,I ,othera portion, derivingfromeacnof said one and lather-.port ns .eerrespedieibut rhese, Opposedinneres,... .tinsihephse Opposed currents `del ,riizedlfrpm said Ciri,anfseidfether rortionsto. 0btain from each thereof. resultant current,differ- I A llymplilldmodulang, the resultant C111'- and the modulationis linear; The same approximation yields the-iinalsimplied. result d Y esteamed-fon 26) If han T3' and half T4' (tubes removed) lee-ri@e .come.unoperative `thecircuit will stilloperate 1f-@msi.aff-1Q.@Qmmmgtthrmwmgdburrents in nals which includes 'these steps,producing alternating current' of substantially fixed carrier frequency,separating the alterating current into two portions of about equalintensity, relatively phase displacing the alternating currents of the inals which includes theseV steps,Y Vproducing alternating current ofsubstantially xed carrier frequency, separating the alterating currentinto first and second portions of aboutequal intensity,

yrelatively phase displacing the alternating cur- -i'ents of the twoportions, deriving from each of lsaid. rst and second portions twocorresponding nportions of Vopposedr polarity, beatingfthe twocorresponding portions derived from each of said first andsecond'p'ortions to derive resultant currents `fromVV each beatingprocess, derivingfrom each of said resultant currents a pair of currentsof opposed phase, differentially amplitude modulating the currents oftle opposed pairs and adding the resultant modulation currents.

6. The method of producing rcarrier I, current modulated as to timing inaccordance with sig-Y nals whichincludes these steps, separating al-Iternating current of substantially fixed frequency,

into'rstandsecond portions of about equal intensity, relatively phasedisplacing the alternating currents of the first and second portions,yderiving from eachof said first and second portions `two' correspondingportions of opposed polarity,

beating, one against the other, the two corresponding portions derivedfrom each of said first andsecond portions to deriveresultant currentsamplitude modulating the currents of the opposed pairs and adding theresultant currents. for signalling purposes. I

7` The method .ofi producing carrier current modulated as to timing inaccordance with signals which includes these stepsr generatingoscillatory energy of substantially xed frequency,

separating the oscillatory energy into two por-f.,

tions, relativelyl phase displacing the oscillatory energies of the twoportions deriving from each of said relatively phased displacedlenergyportions other energies of opposed phase, mixing and multiplyingthe frequency of the oscillatory Y energies' oieach of the two `opposedenergy por# tions Ylike amounts, selecting from the multiplied Yenergies the sum or double frequency energies .resulting from eachmixing step, differentially amplitude modulatingthe ,last-mentionedportions of `frequency multiplied oscillatory energy and adding theresulting energies algebraically.

8.. In combination a source of oscillatory energy of xedvfrequency, twofrequency multiplier tubes .having like factors of multiplication, acoupling .betweensaid source and .one tube, a coupling between saidsource and the lother tube, means Vin one of saidcouplings fordisplacing the phase ofthe oscillatory. energy passed therebyfa firstVV[modulator stage comprising two tubesY coupled "dilferentially to oneof said multiplier tubes, a'

l ofmultiplied frequency from each beating proc-,. ess, deriving from-each of said resultant c urrentsl -afpair of .currents of opposedphase, differentially "aivaso 12 second modulator stage comprisingtwotubes coupled differentially to the other multiplier tube, a common loadimpedance ,coupling the output of said modulator tubes in parallel, anda source of modulating potential'coupled to the modulator tubes. A

9. In combination a source of oscillatory energy of fixed frequency, twoelectron discharge devices, a coupling between said Ysource and onedevice, a coupling between said source and the other device, meansin oneof "said couplings for displacing the phase of the oscillatory energypassed thereby, a first two tube `modulating stage having ran inputcoupled differentially to one of said devices, a second two tubemodulator'stage having an input coupled differentially to the other ofsaid devices, a common load impedance coupling the outputs of all ofsaid modulator tubes in parallel, and a source of modulating potential.differentially coupled to the modulator tubes in veachV stage. Y

l0. In a timing modulation system in combination, a source ofalternating current of fixed -frequency, two converter tubes operatingon the linear parts of the characteristic curves, two couplings betweensaid source and one tube, a current phase reverser in one of saidcouplings, two couplings between said source and the other tube, a phaseshifter in both of said last two couplings and a current phase reverserin one of said last Vtwo couplings, a rst modulator stage coupled to theoutput of one of said converter tubes, a second modulator stage coupledto the output of the other converter tube, a common load impedancecoupling the output of said modulator stages in parallel, and asourcelof modulating potential differentially coupled to the modulatorstages.

11. In a timing modulation system in combina,- tion, a source ofalternating current of xed frequency, two converter tubes operating onthe linear parts of their characteristic l curves, two couplings betweensaid source and one tube, a current phase reverserin one of saidcouplings, two couplings between said source and the other tube, ayphase shifter in both 4of said last two couplings and a currentphasereverser'in one said last two couplings, a rst pair of modulator tubescoupled differentially .to the output of one said converter tubes, asecond pair of modulator tubes coupled differentially to the output ofthe other converter tube, a common loadimpedance coupling the outputs ofsaid modulator tubes in parallel, and a source of modulating potentialdifferentially coupled to the modulator tubes of each pair. Y v

12. In a timing'modulation system in combination, a source ofalternating current of xed frequency, two converter and currentfrequency multiplier tubes operating on the linear parts of Vtheircharacteristic curves,`said frequency multiplier tubes being operated tomultiply the frequency ofthe currents like amounts, two couplingsbetween said source and one tube, a current phase reverser in one ofsaid couplings, two couplings between said source and the other tube, aphase shifter in'both of said last two couplings and a current phasereverser in one of. said last two couplings, a first modulator stagecoupled to the output of one of said converter tubes, a second modulatorstage coupled to the output of the other converter tube, acommon loadimpedance coupling the output of said modulator stages in parallel, anda source of modulating potential differentially coupled to the modulatorstages.

13. In a signalling system, a source of oscillatory system of fixedfrequency, a pair of linear ampliers having input and output electrodes,couplings between said source and the input electrodes of each of saidamplifiers, a phase shifter in one of said couplings, a pair offrequency multiplier tubes of the multi-grid type, a push-pull couplingbetween the output electrodes of one of the ampliers and two grids ofone of the multiplier tubes, a push-pull coupling between the outputelectrodes of the other amplier and two of the grids of the othermultiplier tube, a source of modulating potential, a first pair ofmodulator tubes of the multi-grid type, a push-pull coupling between theoutput electrodes of one of said multiplier tubes and correspondinggrids of said first pair of modulator tubes, a pushpull coupling betweensaid source of modulating potential and corresponding grids in saidfirst pair of modulator tubes, a pull second pair of modulator tubes ofthe multi-grid type, a pushpull coupling between the output of other ofsaid multiplier tubes and corresponding grids in the tubes of saidsecond pair of modulator tubes, a push-pull coupling between :saidsource of modulating potential and corresponding grids of said secondpair of modulator tubes, a load impedance and means coupling the outputelectrodes of the tubes of each pair of modulator tubes in parallel tosaid load impedance.

14. In a signalling system, a source of oscillatory energy of fixedfrequency, a pair of linear amplifiers having input and outputelectrodes, couplings between said source and the input electrodes ofeach of said amplifiers, a phase shifter in one of said couplings, apair of frequency multiplier tubes of the multi-grid type, a push-pullcoupling between the output electrodes of one of the amplifiers and twogrids of one of the multiplier tubes, a push-pull coupling between theoutput electrodes of the other amplier and two of the grids of the othermultiplier tube, a source of modulating potential, a pair of modulatortubes of the multi-grid type, couplings between the output electrodes ofthe respective multiplier tubes and corresponding grids of the tubes ofsaid pair of modulator tubes, a push-pull coupling between said sourceof modulating potentials and other corresponding grids of the tubes ofsaid pair of modulator tubes, a load impedance and means coupling theoutput electrodes of the tubes of said pair of modulator tubes inparallel to said load impedance.

LOWELL E. NORTON.

REFERENCES CITED The following references are of record in the flle ofthis patent:

UNITED STATES PATENTS Number Name Date 2,151,464 Curtis Mar. 21, 19392,210,968 Wirkler Aug. 13, 1940 2,250,296 Crosby July 22, 1941 2,318,934Evans May 11, 1943 2,347,458 Brown Apr. 25, 1944

